The MT2 receptor is a principal type of G protein-coupled receptor that mainly mediates the effects of melatonin. Deficits of melatonin/MT2 signaling have been found in many neurological disorders, including Alzheimer's disease, the most common cause of dementia in the elderly, suggesting that preservation of the MT2 receptor may be beneficial to these neurological disorders. However, direct evidence linking the MT2 receptor to cognition-related synaptic plasticity remains to be established. Here, we report that the MT2 receptor, but not the MT1 receptor, is essential for axonogenesis both 試験管内でとインビボ。 軸索形成は、MT2受容体ノックアウトマウス、MT2 - shRNAエレクトロポレーション脳スライス、またはMT2受容体選択的アンタゴニストで処理された一次ニューロンで遅延することがわかります。 MT2受容体の活性化は、中枢ニューロンの興奮性シナプス伝達の増強に関連する軸索形成を促進します。 MT2受容体の下流のシグナル伝達成分はAkt/GSK-3で構成されています / CRMP-2カスケード。 MT2受容体C-末端モチーフはAktに直接結合します。 MT2受容体の阻害またはMT2受容体-Akt結合の破壊は、軸索形成とシナプス伝達を低下させます。 私たちのデータは、MT2受容体がAkt/GSK-3を活性化することを示唆しています / CRMP-2シグナル伝達は、中枢ニューロンの機能的軸索形成とシナプス形成を仲介するために必要かつ十分です。
Synaptic circuits are established at the sites of axon–dendritic, axon–somatic, or axon–axonal contact, in which functional axonogenesis is a critical step. Axonogenesis can be regulated by many intracellular signals that involve cytoskeletal rearrangements, local protein degradation, as well as diffusional barriers. Additionally, several extracellular neurotrophic factors and hormones have also been shown to have a role in axon guidance and synaptic formation in central neurons. To date, the role of melatonin and its receptors in axonogenesis remains unclear. Most of the biological functions of melatonin are mediated by its two receptors, MT1 and MT2 receptors, both of them belong to the G protein-coupled receptor (GPCR) subfamily and are widely expressed throughout the central nervous system (CNS). Activation of the MT2 receptor in response to melatonin is critical for controlling circadian rhythms and regulation of slow-wave sleep. Early studies have shown that activation of the MT2 receptor in the retina reduces the release of dopamine, while dopamine inhibits growth cone motility and neurite outgrowth during embryonic development, suggesting the involvement of the MT2 receptor in functional axonogenesis. In mutant mice with deficient expression of the MT2 gene, the induction of long-term potentiation (LTP) of excitatory synaptic transmission is impaired, and this impairment is closely related to deficits in learning. In the hippocampus, the MT2 receptor inhibits GABAA receptor-mediated current, which is implicated in synaptic transmission. In Alzheimer's disease, expression of the MT2 receptor is significantly reduced, especially in the hippocampus. A partial agonist of the MT2 receptor, UCM765, exhibits anxiolytic-like properties by increasing the time spent in the open arm of an elevated plus-maze test, and by reducing the latency to eat in a novel environment in the novelty suppressed feeding test, suggesting its role in anxiety. Together, these findings suggest that the MT2 receptor links the signaling cascades that mediate learning and memory formation, one of the important biological functions of melatonin; however, the cellular and molecular events underlying this linkage are yet to be established.
解離した海馬ニューロンは、優れたものとして一般的に使用されています試験管内で海馬ニューロンの形態学的、機能的、および分子的特性を維持するため、軸索発達およびシナプス伝達の研究におけるモデルインビボ。 In dissociated hippocampal neurons, the transition for axon formation and maturation involves the following five stages: stage 1 neurons (2 to 4 h after plating) display abundant lamellipodia and filopodia that develop into several immature short neurites at stage 2 (12 to 24 h); polarization occurs at stage 3 (24 to 48 h), in which a single neurite initiates a rapid elongation to become the axon while others acquire dendritic identity; stage 4 (3–4 days) is characterized by rapid outgrowth of axon and dendrites; and at stage 5 (7 days onwards), the maturation of axon and dendrites is essential for functional synapse formation. In the present study, we have identified a novel role for the MT2 receptor in functional axonogenesis and show that activation of the MT2 receptor is crucial for functional axonogenesis and synaptic transmission in central neurons. Using fluorescence resonance energy transfer (FRET) imaging combined with peptide blocking assays, we have identified Akt as an interacting partner and a substrate of the MT2 receptor. Activation of the MT2 receptor-Akt signaling cascade promotes the formation of functional synapses in the hippocampus, whereas inhibition of the MT2 receptor arrests axonogenesis and synaptic transmission. Given the implications of the MT2 receptor in learning and memory, we propose that targeting MT2 receptor-Akt signaling may be a feasible strategy for stimulating functional synaptic circuit assembly.
分極した軸索におけるMT2受容体の蓄積
軸索発達におけるMT1およびMT2受容体の役割を調査するために、まず、MT1受容体またはMT2受容体とニューロン-特異的Tuj1を共免疫染色することにより、解離したラット海馬ニューロンにおける細胞局在を測定しました。クラスIII -チューブリン。 MT2受容体は、ステージ2ニューロンの先端が濃縮されたすべての神経突起に均一に分布し、強い蛍光シグナルは分極した軸索先端でのみ検出され、ステージ3ニューロンの樹状突起では検出されなかったことがわかりました。 定量分析は、MT2受容体がステージ2ニューロンの神経突起先端で異なって濃縮されたのに対し、MT2受容体のより排他的な軸索先端濃縮がステージ3ニューロンで観察されたことを示しました。 MT1受容体はステージ2でMT2受容体と同様の分布を示しましたが、ステージ3ではMT1受容体の分極分布は検出されませんでした。MT2受容体抗体の特異性はペプチドブロッキング実験によって確認されました。 これらの結果は、MT2受容体がシナプス発達の初期段階である軸索分化に潜在的な役割を果たしている可能性があることを示唆しています。